The present invention relates to electronic circuits for use in automobiles and in particular, to an apparatus and method for processing automotive electronic signals during periods of low system voltage.
In recent years, the number of electronic signals in an automobile has increased dramatically. This large number of signals is managed through the use of signal integration hubs having connectors for receiving conductors from a wide variety of sensors and actuators, and a microprocessor for processing such signals. The automobile instrument cluster is one site used as a signal integration hub because a large number of actuators, such as electronic gauges, lamps and chimes that are found there and because it is in a protected location in the instrument panel near the engine compartment. Other locations for signal integration hub locations are also possible.
While starting the automobile engine or at other times of high current demand, the standard system voltage of approximately twelve volts may drop. A low system voltage may affect digital input circuits and the output of automotive sensors that rely on this voltage as an implicit reference. In these input circuits and sensors as the system voltage drops, the state of the digital input or the output from the sensor may change. System voltage induced changes may be interpreted by a microcontroller at the signal integration hub as a change of state in the sensed quantity and may result in the erroneous control of actuators.
The electronic signals in an automobile may be divided loosely into "convenience signals" intended to enhance or simplify the operation of the automobile or make its use more enjoyable, and "required function signals" associated with safety or legally mandated equipment. Whereas the convenience signals may tolerate momentary interruption during low system voltage conditions, the required function signals are less accommodating of interruption and are designed to operate even at low system voltages.
Normally, the cost of providing error-free low-voltage operation is not justified for convenience signals. Nevertheless, because both convenience and required function signals are typically mixed at a single integration hub, manufacturers face the prospect of either providing low voltage compensation circuitry for all types of signals, or accepting occasional erroneous signals from unprotected convenience signals during periods of low system voltage. These spurious signals may produce harmless but false activations of chimes, bulbs, gauges and the like.